Glomerular filtration and volume regulation in gravid animal models

A simple, inexpensive and portable on-farm test for pregnancy diagnosis and ovary status in cows via chemical analysis of urine

Ovary dysfunction causes an aberrant endocrine surge at various reproductive cycle stages, negatively impacting fertility and economic profit. Optimizing dairy cow performance requires determining ovarian status and detecting early pregnancy. Still, little to no information is available about the diagnosis of the ovarian condition using urine chemical analysis at the field level in Bangladesh. This study aimed to develop a simple, inexpensive and portable on-farm technique for pregnancy diagnosis and ovary status determination in cows via chemical urine analysis. Fifty reproductively healthy cows were recruited from different donor farms. Prior to artificial insemination (AI), all selected cows were placed in a single ovsynch program. TAI (timed artificial insemination) was carried out. Urine was routinely collected from Day 0-55 days at estrus cycle stages for routine chemical analysis using barium chloride (BaCl2), followed by commercially available protein strip tests. The developed techniques for pregnancy and ovary status diagnosis in cows were validated with rectal palpation (RP). Barium chloride (BaCl2) analysis of urine revealed white precipitation corresponding to a mature follicle in the ovary during estrus and colorless precipitation corresponding to the corpus luteum during the diestrus period. Positive pregnancy was indicated by the presence of a colorless precipitate in the BaCl2 test, and a protein value of less than 100 mg/dl was found in the protein strip test. The maximum accuracy (42/50, 84%) was observed between 25 and 35 days, as confirmed by RP. Perplexing results were seen 45-55 days after AI, between pregnancies and luteal cystic disease. In both cases, we discovered that the BaCl2 precipitation was colorless. However, the protein value in the context of luteal cystic disease was found to be higher than 100 mg/dl. The barium chloride test, followed by protein strip tests, is a simple and portable way to diagnose pregnancy and determine ovarian status in cows at the field level.

Mathematical modeling of calcium homeostasis in female rats: An analysis of sex differences and maternal adaptations

Calcium plays a vital role in various biological processes, including muscle contractions, blood clotting, skeletal mineralization, and cell signaling. While extracellular calcium makes up less than 1% of total body calcium, it is tightly regulated since too high or too low extracellular calcium concentration can have dangerous effects on the body. Mathematical modeling is a well-suited approach to investigate the complex physiological processes involved in calcium regulation. While mathematical models have been developed to study calcium homeostasis in male rats, none have been used to investigate known sex differences in hormone levels nor the unique physiological states of pregnancy and lactation. Calcitriol, the active form of vitamin D, plays a key role in intestinal calcium absorption, renal calcium reabsorption, and bone remodeling. It has been shown that, when compared to age-matched male rats, females have significantly lower calcitriol levels. In this study we first seek to investigate the impact of this difference as well as other known sex differences on calcium homeostasis using mathematical modeling. Female bodies differ from male bodies in that during their lifetime they may undergo massive adaptations during pregnancy and lactation. Indeed, maternal adaptations impact calcium regulation in all mammals. In pregnant rodents, intestinal absorption of calcium is massively increased in the mother's body to meet the needs of the developing fetus. In a lactating rodent, much of the calcium needs of milk are met by bone resorption, intestinal absorption, and renal calcium reabsorption. Given these observations, the goal of this project is to develop multi-scale whole-body models of calcium homeostasis that represents (1) how sex differences impact calcium homeostasis in female vs. male rats and (2) how a female body adapts to support the excess demands brought on by pregnancy and lactation. We used these models to quantify the impact of individual sex differences as well as maternal adaptations during pregnancy and lactation. Additionally, we conducted "what if" simulations to test whether sex differences in calcium regulation may enable females to better undergo maternal adaptations required in pregnancy and lactation than males.

Modeling renal autoregulation in a hemodynamic, first-trimester gestational model

The maternal cardiovascular system, led by renal volume regulatory responses, changes during pregnancy to ensure an adequate circulation for fetal development and growth. Circulatory maladjustment predisposes to hypertensive complications during pregnancy. Mathematical models can be used to gain insight in the gestational cardiovascular physiology. In this study, we developed an accurate, robust, and transparent model for renal autoregulation implemented in an existing circulatory gestational model. This renal autoregulation model aims to maintain steady glomerular pressure by the myogenic response, and glomerular filtration rate by tubuloglomerular feedback, both by inducing a change in the radius, and thus resistance, of the afferent arteriole. The modeled response of renal blood flow and the afferent arteriole following blood pressure increase were compared to published observations in rats. With solely the myogenic response, our model had a maximum deviation of 7% in change in renal blood flow and 7% in renal vascular resistance. When both the myogenic response and tubuloglomerular feedback were concurrently activated, the maximum deviation was 7% in change in renal blood flow and 5% in renal vascular resistance. These results show that our model is able to represent renal autoregulatory behavior comparable to empirical data. Further studies should focus on extending the model with other regulatory mechanisms to understand the hemodynamic changes in healthy and complicated pregnancy.

Glomerular hyperfiltration

Circulating blood is filtered across the glomerular barrier to form an ultrafiltrate of plasma in the Bowman's space. The volume of glomerular filtration adjusted by time is defined as the glomerular filtration rate (GFR), and the total GFR is the sum of all single-nephron GFRs. Thus, when the single-nephron GFR is increased in the context of a normal number of functioning nephrons, single glomerular hyperfiltration results in 'absolute' hyperfiltration in the kidney. 'Absolute' hyperfiltration can occur in healthy people after high protein intake, during pregnancy and in patients with diabetes, obesity or autosomal-dominant polycystic kidney disease. When the number of functioning nephrons is reduced, single-nephron glomerular hyperfiltration can result in a GFR that is within or below the normal range. This 'relative' hyperfiltration can occur in patients with a congenitally reduced nephron number or with an acquired reduction in nephron mass consequent to surgery or kidney disease. Improved understanding of the mechanisms that underlie 'absolute' and 'relative' glomerular hyperfiltration in different clinical settings, and of whether and how the single-nephron haemodynamic and related biomechanical forces that underlie glomerular hyperfiltration promote glomerular injury, will pave the way toward the development of novel therapeutic interventions that attenuate glomerular hyperfiltration and potentially prevent or limit consequent progressive kidney injury and loss of function.

No evidence of the unfolded protein response in the placenta of two rodent models of preeclampsia and intrauterine growth restriction

In humans, intrauterine growth restriction (IUGR) and preeclampsia (PE) are associated with induction of the unfolded protein response (UPR) and increased placental endoplasmic reticulum (ER) stress. Especially in PE, oxidative stress occurs relative to the severity of maternal vascular underperfusion (MVU) of the placental bed. On the premise that understanding the mechanisms of placental dysfunction could lead to targeted therapeutic options for human IUGR and PE, we investigated the roles of the placental UPR and oxidative stress in two rodent models of these human gestational pathologies. We employed a rat IUGR model of gestational maternal protein restriction, as well as an endothelial nitric oxide synthase knockout mouse model (eNOS-/-) of PE/IUGR. Placental expression of UPR members was analyzed via qRT-PCR (Grp78, Calnexin, Perk, Chop, Atf6, and Ern1), immunohistochemistry, and Western blotting (Calnexin, ATF6, GRP78, CHOP, phospho-eIF2α, and phospho-IRE1). Oxidative stress was determined via Western blotting (3-nitrotyrosine and 4-hydroxy-2-nonenal). Both animal models showed a significant reduction of fetal and placental weight. These effects did not induce placental UPR. In contrast to human data, results from our rodent models suggest retention of placental plasticity in the setting of ER stress under an adverse gestational environment. Oxidative stress was significantly increased only in female IUGR rat placentas, suggesting a sexually dimorphic response to maternal malnutrition. Our study advances understanding of the involvement of the placental UPR in IUGR and PE. Moreover, it emphasizes the appropriate choice of animal models researching various aspects of these pregnancy complications.

Kidney Physiology in Pregnancy

A woman's body undergoes a myriad of changes throughout the course of a normal gestation. The kidneys play a central role in driving adjustments that guarantee maternal and fetal well-being, including a dramatic increase in glomerular filtration rate, alterations in tubular function, and changes in electrolyte and acid/base handling. Early in gestation, systemic vasodilation, driven by both a change in quantity of and response to various hormones, leads to increased renal blood flow and glomerular filtration rate. Vasodilation also results in activation of the renin-angiotensin-aldosterone axis, which combined with changing tubular handling causes alterations in total body stores of electrolytes and total body water, resulting in a lower serum sodium concentration. In addition, mild proteinuria, glucosuria, and a decrease in serum calcium and magnesium are common. The primary acid/base change seen in pregnancy is a mild respiratory alkalosis due to progesterone effects. This article provides an overview of the current understanding of the healthy response of the kidneys to pregnancy, an understanding of which is key to caring for the pregnant patient, and early identification of alterations that may indicate underlying kidney pathology in pregnancy.

The enigma of continual plasma volume expansion in pregnancy: critical role of the renin-angiotensin-aldosterone system

Pregnancy is characterized by avid renal sodium retention and plasma volume expansion in the presence of decreased blood pressure. Decreased maternal blood pressure is a consequence of reduced systemic vascular tone, which results from an increased production of vasodilators [nitric oxide (NO), prostaglandins, and relaxin] and decreased vascular responsiveness to the potent vasoconstrictor (angiotensin II). The kidneys participate in this vasodilatory response, resulting in marked increases in renal plasma flow and glomerular filtration rate (GFR) during pregnancy. In women, sodium retention drives plasma volume expansion (∼40%) and is necessary for perfusion of the growing uterus and fetus. For there to be avid sodium retention in the presence of the potent natriuretic influences of increased NO and elevated GFR, there must be modifications of the tubules to prevent salt wasting. The purpose of this review is to summarize these adaptations.

Maternal Mineral and Bone Metabolism During Pregnancy, Lactation, and Post-Weaning Recovery

During pregnancy and lactation, female physiology adapts to meet the added nutritional demands of fetuses and neonates. An average full-term fetus contains ∼30 g calcium, 20 g phosphorus, and 0.8 g magnesium. About 80% of mineral is accreted during the third trimester; calcium transfers at 300-350 mg/day during the final 6 wk. The neonate requires 200 mg calcium daily from milk during the first 6 mo, and 120 mg calcium from milk during the second 6 mo (additional calcium comes from solid foods). Calcium transfers can be more than double and triple these values, respectively, in women who nurse twins and triplets. About 25% of dietary calcium is normally absorbed in healthy adults. Average maternal calcium intakes in American and Canadian women are insufficient to meet the fetal and neonatal calcium requirements if normal efficiency of intestinal calcium absorption is relied upon. However, several adaptations are invoked to meet the fetal and neonatal demands for mineral without requiring increased intakes by the mother. During pregnancy the efficiency of intestinal calcium absorption doubles, whereas during lactation the maternal skeleton is resorbed to provide calcium for milk. This review addresses our current knowledge regarding maternal adaptations in mineral and skeletal homeostasis that occur during pregnancy, lactation, and post-weaning recovery. Also considered are the impacts that these adaptations have on biochemical and hormonal parameters of mineral homeostasis, the consequences for long-term skeletal health, and the presentation and management of disorders of mineral and bone metabolism.

Chronic Nicotine Exposure Abolishes Maternal Systemic and Renal Adaptations to Pregnancy in Rats

Pregnancy is characterized by maternal systemic and intrarenal vasodilation, leading to increases in the renal plasma flow (RPF) and glomerular filtration rate (GFR). These responses are mainly mediated by nitric oxide (NO) and relaxin. The impact of cigarette smoking on the maternal adaptations to pregnancy is unclear. Here we evaluated the effects of chronic exposure to nicotine on systemic and intrarenal parameters in virgin (V) and 14-day pregnant (P) Wistar rats. V and P groups received saline or nicotine (6 mg·kg^-1·day^-1) respectively, via osmotic minipumps for 28 days, starting 14 days before pregnancy induction. Nicotine induced a 10% increase in blood pressure in the V group and minimized the characteristic pregnancy-induced hypotension. Renal sympathetic nerve activity (rSNA) and baroreflex sensitivity were impaired by nicotine mainly in the P group, indicating that the effect of nicotine on blood pressure was not mediated by nervous system stimulation. Nicotine had no effect on GFR in the V rats but reduced GFR of the P group by 30%. Renal expression of sodium and water transporters was downregulated by nicotine, resulting in increased fractional sodium excretion mainly in the P group, suggesting that nicotine compromised the sodium and water retention required for normal gestation. There was a reduction in the expression of inducible NO synthase (iNOS) in both the kidney tissue and renal artery, as well as in the expression of the relaxin receptor (LGR7). These results clearly show that nicotine induced deleterious effects in both virgin and pregnant animals, and abolished the maternal capacity to adapt to pregnancy.

Pregnant rats treated with a high-fat/prooxidant Western diet with ANG II and TNF-α are resistant to elevations in blood pressure and renal oxidative stress

Oxidative stress and inflammation are risk factors for hypertension in pregnancy. Here, we examined the 24-h mean arterial pressure (MAP) via telemetry and the nitric oxide (NO) and redox systems in the kidney cortex, medulla, and aorta of virgin and pregnant rats treated with a high-fat/prooxidant Western diet (HFD), ANG II, and TNF-α. Female Sprague-Dawley rats were given a normal diet (ND) or a HFD for 8 wk before mating. Day 6 of pregnancy and age-matched virgins were implanted with minipumps infusing saline or ANG II (150 ng·kg(-1)·min(-1)) + TNF-α (75 ng/day) for 14 days. Groups consisted of Virgin + ND + Saline (V+ND) (n = 7), Virgin + HFD +ANG II and TNF-α (V+HFD) (n = 7), Pregnant + ND + Saline (P+ND) (n = 6), and Pregnant + HFD + ANG II and TNF-α (P+HFD) (n = 8). After day 6 of minipump implantation, V+HFD rats displayed an increase in MAP on days 7, 8, and 10-15 vs. V+ND rats. P+HFD rats, after day 6 of minipump implantation, showed an increase in MAP only on day 7 vs. P+ND rats. P+HFD rats had a normal fall in 24-h MAP, hematocrit, plasma protein concentration, and osmolality at late pregnancy. No change in kidney cortex, medulla, or aortic oxidative stress in P+HFD rats. P+HFD rats displayed a decrease in nNOSβ abundance, but no change in kidney cortex NOx content vs. P+ND rats. Pregnant rats subjected to a chronic HFD and prooxidant and proinflammatory insults have a blunted increase in 24-h MAP and renal oxidative stress. Our data suggest renal NO bioavailability is not altered in pregnant rats treated with a HFD, ANG II, and TNF-α.

Chronic vasodilation increases renal medullary PDE5A and α-ENaC through independent renin-angiotensin-aldosterone system pathways

We have previously observed that many of the renal and hemodynamic adaptations seen in normal pregnancy can be induced in virgin female rats by chronic systemic vasodilation. Fourteen-day vasodilation with sodium nitrite or nifedipine (NIF) produced plasma volume expansion (PVE), hemodilution, and increased renal medullary phosphodiesterase 5A (PDE5A) protein. The present study examined the role of the renin-angiotensin-aldosterone system (RAAS) in this mechanism. Virgin females were treated for 14 days with NIF (10 mg·kg(-1)·day(-1) via diet), NIF with spironolactone [SPR; mineralocorticoid receptor (MR) blocker, 200-300 mg·kg(-1)·day(-1) via diet], NIF with losartan [LOS; angiotensin type 1 (AT1) receptor blocker, 20 mg·kg(-1)·day(-1) via diet], enalapril (ENAL; angiotensin-converting enzyme inhibitor, 62.5 mg/l via water), or vehicle (CON). Mean arterial pressure (MAP) was reduced 7.4 ± 0.5% with NIF, 6.33 ± 0.5% with NIF + SPR, 13.3 ± 0.9% with NIF + LOS, and 12.0 ± 0.4% with ENAL vs. baseline MAP. Compared with CON (3.6 ± 0.3%), plasma volume factored for body weight was increased by NIF (5.2 ± 0.4%) treatment but not by NIF + SPR (4.3 ± 0.3%), NIF + LOS (3.6 ± 0.1%), or ENAL (4.0 ± 0.3%). NIF increased PDE5A protein abundance in the renal inner medulla, and SPR did not prevent this increase (188 ± 16 and 204 ± 22% of CON, respectively). NIF increased the α-subunit of the epithelial sodium channel (α-ENaC) protein in renal outer (365 ± 44%) and inner (526 ± 83%) medulla, and SPR prevented these changes. There was no change in either PDE5A or α-ENaC abundance vs. CON in rats treated with NIF + LOS or ENAL. These data indicate that the PVE and renal medullary adaptations in response to chronic vasodilation result from RAAS signaling, with increases in PDE5A mediated through AT1 receptor and α-ENaC through the MR.

Decreased expression of a novel prostaglandin transporter, OAT-PG, facilitates renocortical PGE2 accumulation during rat pregnancy

BACKGROUND

Prostaglandin (PG)-specific organic anion transporter (OAT-PG) is a recently identified renal transporter involved in the local clearance of prostaglandin E2 (PGE2). Since the renal biosynthesis of PGE2 is not increased during pregnancy, this transporter expression would affect the gestational changes in the renal PGE2 content.

METHODS

Kidneys from rats at different gestational stages were used to examine gestational changes in the renocortical PGE2 concentration. The renal expression of OAT-PG and the enzymes for PGE2 synthesis was also examined sequentially, together with the gestational changes in renal renin production.

RESULTS

The renocortical PGE2 concentration was significantly increased during midterm to late pregnancy, with a maximum increase of 47.6 ± 11.5% from the virgin value. Although the expression of the enzymes, such as cyclooxygenases and PG synthases, was not increased, that of OAT-PG was significantly decreased throughout pregnancy, inversely correlating with changes in the renocortical PGE2 concentration. Renal renin production was significantly increased during pregnancy.

CONCLUSION

This study demonstrated for the first time that the tissue PGE2 concentration was increased in pregnant rat kidneys, which may be associated with the gestational rise in glomerular filtration rate. The decreased expression of OAT-PG was thought to be responsible for the increased tissue PGE2 content.

Renal redox response to normal pregnancy in the rat

Normal pregnancy involves increased renal sodium reabsorption, metabolism, and oxygen consumption, which can cause increased oxidative stress (OS). OS can decrease nitric oxide (NO) bioavailability and cause pregnancy complications. In this study we examined the NO synthases (NOS) and redox state in the kidney cortex and aorta in early (E), mid (M), and late (L) pregnant (P) (days 3, 12, 20) and 2-4 days postpartum (PP) rats compared with virgin rats (V). Protein abundance of endothelial NOS (eNOS) was unchanged and neuronal NOS (nNOS)α fell at LP in the kidney cortex. Kidney cortex nNOSβ was elevated at MP, LP, and PP. No changes in aortic NOS isoforms were observed. Kidney cortex nitrotyrosine (NT) abundance decreased in EP, MP, and PP, whereas aortic NT increased in EP, MP, and PP. The NADPH oxidase subunit p22phox decreased in the kidney cortex at EP while aortic p22phox increased in EP and LP. No changes in kidney cortex NADPH-dependent superoxide production or hydrogen peroxide levels were noted. Kidney cortex cytosolic (CuZn) superoxide dismutase (SOD) was unchanged, while mitochondrial SOD decreased at EP and extracellular SOD decreased at MP and LP in the kidney cortex. Despite falls in abundance of kidney cortex SODs, total antioxidant capacity (TAC) was elevated in EP, MP, and PP in the kidney cortex. Aortic CuZn SOD deceased at PP, while the other aortic SODs and aortic TAC did not change. Data from this study suggest that the kidney cortex is protected from OS during normal rat pregnancy via an increase in antioxidant activity.

Correlação entre cálcio e insulina durante o teste de tolerância à glicose em ovelhas gestantes e não gestantes

Compararam-se as concentrações de cálcio, glicose e insulina em ovelhas gestantes e não gestantes submetidas ao teste de tolerância à glicose (TTG). Oito ovelhas gestantes (GG) e oito não gestantes (NG) foram submetidas ao TTG por meio da administração endovenosa de uma solução de glicose, na dose de 500mg/kg de peso vivo. Amostras de sangue foram coletadas nos tempos de -15, zero, 15, 30, 45, 60, 90, 120, 150 e 180 minutos, sendo zero min o momento da infusão, para avaliação da concentração sanguínea de glicose, cálcio e insulina. Foi avaliada a taxa de metabolização de glicose e insulina, por meio do cálculo da área sob a curva (ASC). As concentrações de glicose, cálcio, insulina e a ASC da insulina não diferiram entre os grupos (P>0,05), entretanto as três últimas ASCs da glicose foram mais elevados nas gestantes (P<0,05), que correspondem ao período entre 90 e 180min. O teste de correlação de Pearson revelou correlação negativa entre concentração de cálcio e insulina nas gestantes (P<0,05). Estes resultados indicam menor taxa de metabolização de glicose em ovelhas gestantes e uma possível relação de cálcio e insulina no terço final de gestação.

Maternal adaptations and inheritance in the transgenerational programming of adult disease

Adverse exposures in utero have long been linked with an increased susceptibility to adult cardio-renal and metabolic diseases. Clear gender differences exist, whereby growth-restricted females, although exhibiting some phenotypic modifications, are often protected from overt disease outcomes. One of the greatest physiological challenges facing the female gender, however, is that of pregnancy; yet little research has focused on the outcomes associated with this, as a potential 'second-hit' for those who were small at birth. We review the limited evidence suggesting that pregnancy may unmask cardio-renal and metabolic disease states and the consequences for long-term maternal health in females who were born small. Additionally, a growing area of research in this programming field is in the transgenerational transmission of low birth weight and disease susceptibility. Pathways for transmission might include an abnormal adaptation to pregnancy by the growth-restricted mother and/or inheritance via the parental germline. Strategies to optimise the pregnancy environment and/or prevent the consequences of inheritance of programmed deficits and dysfunction are of critical importance for future generations.

Update on pregnancy in chronic kidney disease

The occurrence of pregnancy in patients with chronic kidney disease (CKD) has been considered a dangerous event both for the mother and for the fetus. However, increasing evidence shows that the stage of CKD is the leading factor that can predict possible acceleration in the declining of renal function and complications of pregnancy. This review summarizes recent data on pregnancy in patients with CKD, dialysis and kidney transplantation.

Chronic vasodilation produces plasma volume expansion and hemodilution in rats: consequences of decreased effective arterial blood volume

Plasma volume (PV) expansion is required for optimal pregnancy outcomes; however, the mechanisms responsible for sodium and water retention in pregnancy remain undefined. This study was designed to test the "arterial underfill hypothesis" of pregnancy which proposes that an enlarged vascular compartment (due to systemic vasodilation and shunting of blood to the placenta) results in renal sodium and water retention and PV expansion. We produced chronic vasodilation by 14 days administration of nifedipine (NIF; 10 mg·kg(-1)·day(-1)) or sodium nitrite (NaNO2; 70 mg·kg(-1)·day(-1)) to normal, nonpregnant female Sprague-Dawley rats. Mean arterial pressure, monitored by telemetry, was reduced by both NIF and NaNO2 but was unchanged in control rats. At day 14, vasodilator treatment lowered hematocrit and increased PV (determined by Evans blue dye dilution). Plasma osmolarity (Posm), sodium (PNa), and total protein concentrations all fell. These responses resemble the responses to normal pregnancy with hemodilution, marked PV expansion, and decreased Posm and PNa. Our previous work indicates a role of increased inner medullary phosphodiesterase-5 (PDE5) in the sodium retention of pregnancy. Here, we found that inner medullary PDE5A mRNA and protein expression were increased by both NIF and NaNO2 treatment vs. control; however, neither renal cortical nor aortic PDE5 expression was changed by vasodilator treatment. We suggest that a primary, persistent vasodilation drives increased inner medullary PDE5 expression which facilitates continual renal Na retention causing "refilling" of the vasculature and volume expansion.

The ouabain-binding site of the α2 isoform of Na,K-ATPase plays a role in blood pressure regulation during pregnancy

BACKGROUND

The cardiotonic steroid/ouabain-binding site of the α subunit of Na,K-ATPase is thought to play an important role in cardiovascular homeostasis. Previously, we demonstrated the cardiotonic steroid-binding site of the α2 Na,K-ATPase is involved in adrenocorticotropic hormone (ACTH)-induced hypertension by using gene-modified α2(R/R) mice in which the cardiotonic steroid-binding site is relatively resistant to ouabain compared to the ouabain-sensitive wild-type α2(S/S) mice. To further explore the importance of this site in the cardiovascular system, we investigated blood pressure regulation during pregnancy in mice with the α2(R/R) isoform.

METHODS

The systolic blood pressure (SBP) of the α2(S/S) and α2(R/R) mice was measured before and during pregnancy by tail-cuff. The expression of the α isoforms of Na, K-ATPase in various tissues and plasma endogenous ouabain contents were assessed prior to pregnancy as well as days 7 and 17 of gestation.

RESULTS

The α2(S/S) mice showed a gradual decrease in the SBP during the first two trimesters, followed by an increase above the preconceptional level in the third trimester. However, the α2(R/R) mice exhibited a lower blood pressure in the third trimester. The cardiac expression of the α2 Na,K-ATPase in the α2(S/S) mice was significantly less than that of the α2(R/R) mice throughout the pregnancy. The plasma endogenous ouabain concentration significantly increased by twofold at day 17 of pregnancy in the α2(R/R) mice but not in the α2(S/S) mice.

CONCLUSIONS

The cardiotonic steroid-binding site of the α2 Na,K-ATPase plays a role in maintaining normal SBP during pregnancy.

Renal nitric oxide production in rat pregnancy: role of constitutive nitric oxide synthases

Functional studies show that increased renal nitric oxide (NO) mediates the renal vasodilation and increased glomerular filtration rate that occur during normal pregnancy. We investigated whether changes in the constitutive NO synthases (NOS), endothelial (eNOS) and neuronal (nNOS), were associated with the increased renal NO production in normal midterm pregnancy in the rat. In kidneys from midterm pregnant (MP: 11-13 days gestation), late-term pregnant (LP: 18-20 days gestation), and similarly aged virgin (V) rats, transcript and protein abundance for eNOS and the nNOSα and nNOSβ splice variants, as well as the rate of L-arginine-to-L-citrulline conversion, were determined as a measure of NOS activity. At MP, renal cortical abundance of the total eNOS protein and phosphorylated (Ser(1177)) eNOS was reduced, and L-arginine-to-L-citrulline conversion in the cortical membrane fraction was decreased; these declines were also seen in LP. There were no changes in the eNOS transcript. In contrast, L-arginine-to-L-citrulline conversion in the soluble fraction of renal cortex increased at MP and then declined at LP. This MP increase was ablated by S-methylthiocitrulline, a nNOS inhibitor. Using Western blotting, we did not detect a change in the protein abundance or transcript of the 160-kDa nNOSα, but protein abundance and transcript of the nNOSβ were increased at MP in cortex. Collectively, these studies suggest that the soluble nNOSβ is responsible for the increased renal cortical NO production during pregnancy.

Increased renal phosphodiesterase-5 activity mediates the blunted natriuretic response to a nitric oxide donor in the pregnant rat

Pregnancy is characterized by plasma volume expansion and renal sodium retention with loss of natriuretic response to atrial natriuretic peptide due to increased medullary phosphodiesterase-5 (PDE5). Here, we determined whether natriuretic responses to nitric oxide (NO) are also blunted in pregnancy due to increased PDE5. Anesthetized 16-day pregnant and virgin rats were studied at baseline and during intrarenal infusion of the NO donor spermine NONOate (2.5 nmol/min), the PDE5 inhibitor sildenafil (SILD; 0.5 μg/min), or a combination. The right (noninfused) kidney served as a control. Intrarenal NONOate had no effect on mean arterial pressure (MAP); however, SILD reduced MAP in virgin rats, and the combination of NONOate+SILD reduced MAP in both virgin and pregnant rats. Neither NONOate nor SILD altered glomerular filtration rate. NONOate and SILD each stimulated sodium excretion (U(Na)V) and fractional excretion of sodium (FE(Na)) in virgin rats, but the combination did not result in an additional natriuretic response. However, NONOate infusion did not increase U(Na)V or FE(Na) in pregnant rats, but the natriuretic response to NONOate was restored with SILD, and SILD alone produced a natriuresis during pregnancy. Sodium nitroprusside (10(-4) mol/l)-stimulated cGMP accumulation from inner medullary collecting duct cells was blunted in cells from pregnant vs. virgin or postpartum rats and was restored by treatment with the PDE5 inhibitor DMPPO (10(-7) mol/l). Therefore, increased intrarenal PDE5 mediates the blunted natriuretic response to NO, and loss of responsiveness to the cGMP-dependent, natriuretic agents may contribute to volume expansion during pregnancy.

Diagnosis and treatment of hypertensive disorders during pregnancy

Pregnancy is a cardiovascular and metabolic challenge to the human female body. This review summarizes current knowledge on the regulation of blood pressure and plasma volume in normal and hypertensive pregnant women. During pregnancy, systemic vascular resistance and blood pressure decrease, whereas cardiac output and blood volume increase to safeguard an adequate circulation in the utero-placental arterial bed. Hypertension affects 10% of all pregnancies and is accompanied by an increase in foetal and maternal morbidity and mortality. Hypertension in pregnancy includes a wide spectrum of conditions, including pre-eclampsia and eclampsia, pre-eclampsia superimposed on chronic hypertension, chronic hypertension, and gestational hypertension. Endothelial dysfunction, oxidative stress and an exaggerated inflammatory response are features related to hypertensive disorders. Microangiopathic disorders can easily mimic hypertensive disorders during pregnancy. Although they have some symptoms in common, they require another type of management. To reduce the risk of maternal and foetal complications due to haemodynamic maladaptations, the current management includes rest at home or in the hospital, close monitoring of maternal and foetal signs and symptoms, early start of antihypertensive therapy, and timely delivery regarding maternal and foetal survival chances. Thresholds to initiate blood pressure lowering treatment during pregnancy are 160 mmHg systole or 110 mmHg diastole. Below these thresholds, treatment must be individualized because current evidence does not support aggressive medical interventions. Alpha-methyldopa and dihydropyridinic calcium channel blockers are among the recommended antihypertensives.

Physiological changes of pregnancy and monitoring

Advances in medical care have led to increasing numbers of complex, high-risk obstetric patients. Specialist training and a sound knowledge of normal maternal physiology are essential to optimize outcomes. One of the earliest observed changes is peripheral vasodilatation; this causes a fall in systemic vascular resistance and triggers physiological changes in the cardiovascular and renal systems, with 40-50% increases in cardiac output and glomerular filtration rates. Safety concerns over Swan Ganz catheters have driven the increasing interest in alternative techniques, such as echocardiography, thoracic bioimpedance and pulse contour analysis, although their exact roles in future obstetric high-dependency care have yet to be established. Analysis of arterial blood gases is fundamental to the management of sick patients, and correct interpretation can be aided by a systematic approach. Observation charts are almost ubiquitous in all aspects of medicine, but little evidence exists to support their use in the high-dependency setting.

The natriuretic and diuretic response to dopamine is maintained during rat pregnancy

During pregnancy, there is a marked plasma volume expansion due to renal sodium retention. Pregnant rats exhibit a blunted response to natriuretic stimuli that signal via cGMP, and expression and activity of the cGMP phosphodiesterase PDE-5 are upregulated in the inner medullary collecting duct during pregnancy. Here, we tested the hypothesis that the natriuretic response to a cAMP agonist, dopamine, is maintained during pregnancy. Anesthetized pregnant (day 16) and age-matched virgin Sprague-Dawley rats were used to determine whether dopamine-cAMP-mediated natriuresis remains intact in pregnant rats. Blood pressure, renal clearances of inulin and p-aminohippuric acid, and excretion of sodium were measured during baseline and dopamine infusion periods. Pregnant rats had a lower blood pressure and hematocrit at baseline than their age-matched virgin counterparts. Dopamine infusion decreased blood pressure and increased glomerular filtration rate and renal plasma flow in virgin but not pregnant rats. Dopamine infusion also increased urine volume, sodium excretion, and the fractional excretion of sodium to a similar extent in virgin and pregnant rats. These results indicate that a cAMP-mediated natriuresis and diuresis (stimulated by dopamine) persists in pregnant rats.

Increased renal phosphodiesterase-5 activity mediates the blunted natriuretic response to ANP in the pregnant rat

Normal rat pregnancy is characterized by plasma volume expansion due to renal sodium retention and is associated with a blunted response to natriuretic stimuli, such as atrial natriuretic peptide (ANP). ANP signals via cGMP, and phosphodiesterases (PDE) inactivate cGMP and terminate the natriuretic response. We previously reported that increased medullary PDE-5 activity occurs in rat pregnancy, which may be the mechanism of the blunted natriuretic effect of ANP. Here, we used anesthetized 16-day pregnant and virgin rats to investigate whether intrarenal infusion of a selective PDE-5 inhibitor, sildenafil, would reverse the blunted response to ANP in pregnancy. We measured blood pressure, renal clearances using inulin and p-aminohippuric acid, and electrolyte excretion at baseline and during an ANP infusion. ANP caused a fall in mean arterial pressure in all groups, and sildenafil induced a further reduction. We observed an increase in sodium excretion with ANP in all rats, but this was blunted in the vehicle-infused pregnant rats. This could not be explained by differences in renal hemodynamics and was of tubular origin, as reflected by the reduced rise in fractional excretion of sodium with ANP in the pregnant rat given vehicle (45 +/- 11 vs. 204 +/- 49%; P < 0.05). However, intrarenal sildenafil increased the natriuretic response and the rise in fractional excretion of sodium to the virgin value (226 +/- 23 vs. 245 +/- 73%; not significant), whereas the blunting persisted in the contralateral kidney. This demonstrates that increased intrarenal PDE-5 mediates the blunted natriuretic response to ANP during pregnancy and may contribute to the physiological volume expansion.

Plasma protein and blood volume restitution after hemorrhage in conscious pregnant and ovarian steroid-replaced rats

We have previously shown that both plasma protein restitution and plasma volume restitution are significantly enhanced in female rats hemorrhaged during the proestrus phase of the estrous cycle. Estradiol and progesterone levels are markedly elevated during proestrus and also increase during pregnancy. The present studies were therefore designed to determine whether the ability to restore plasma protein and blood volume after hemorrhage is augmented during pregnancy and by chronically elevated estradiol levels. The response to moderate hemorrhage (22–23% blood loss) was evaluated in conscious pregnant rats during early and midgestation and compared with that of virgin female rats studied during metestrus. At 22 h posthemorrhage, plasma volume had increased to greater than basal levels, and blood volume was restored to 93 ± 1% (metestrus), 91 ± 2% (early pregnancy), and 98 ± 2% (midgestation) of control ( P > 0.05). Animals hemorrhaged during metestrus or early pregnancy restored the same amount of protein to the plasma as had been removed, whereas those hemorrhaged during midgestation restored nearly 50% more plasma protein than had been removed ( P < 0.01). In ovariectomized animals with chronic steroid replacement that maintained plasma progesterone at metestrus levels (15 ± 2 ng/ml) but raised plasma estradiol to twofold that of midgestation (22 ± 3 pg/ml), the blood volume and plasma protein restitution responses to hemorrhage did not differ from those of ovariectomized animals with no steroid replacement. In summary, posthemorrhage restoration of plasma protein content is significantly augmented during midgestation, but not during early pregnancy. This augmented response cannot be attributed to chronic elevation of plasma estradiol levels alone.

Unwanted Pregnancy Among Kidney Transplant Recipients in Iran

To investigate the incidence of unwanted pregnancy among kidney transplant recipients, we studied 86 pregnancies in 64 women with a transplanted kidney. Twenty-five pregnancies were unwanted (29.1%). Pregnancy was terminated by induced abortion in seven patients, and four pregnancies were lost due to spontaneous abortion with one intrauterine fetal death. Only 13 (52%) pregnancies resulted in a live birth. Most of the unwanted pregnancies occurred in women using coitus interruptus (92%) as the only method of contraception. It is concluded that because fertility greatly improves after kidney transplantation, it is necessary to have a family planning counseling session before surgery. If a patient is not interested in future pregnancy, an effective method of contraception should be offered. A woman who has decided against childbearing in the future may decide to have a tubal ligation at the time of transplantation surgery.

Glomerular structural changes in pregnant, diabetic, and pregnant-diabetic rats

Kidneys enlarge both during pregnancy and in diabetes. The enlargement and morphology of glomeruli was studied during pregnancy and in diabetes in order to examine possible similarities, differences, and interactions in the growth in these conditions. Morphometric investigations were performed on glomeruli in pregnant rats, in rats with 2 weeks' diabetes, and in pregnant-diabetic rats. Kidneys were enlarged 22% in the midterm pregnant rats compared with controls, 74% in diabetic rats, and a further 21% in pregnant-diabetic rats. Glomerular volume was enlarged by 26% during midterm pregnancy in normal animals. Diabetes induced an enlargement in glomerular volume of 58% and a further 18% in midterm diabetic animals due to pregnancy. Within the glomerulus, pregnancy in normal animals induced minor non-significant changes. Diabetes induced significant increase in several parameters: mesangial volume and cell volume, capillary and glomerular basement membrane volume, capillary wall surface area, foot process width, filtration slit length, and nuclear number. Pregnancy in diabetic animals induced no significant additional changes. In conclusion, kidney enlargement in pregnancy shows very few glomerular changes in either normal or diabetic animals. Enlargement of glomeruli in diabetes involves hypertrophy and hyperplasia concurrent with several morphological changes within the glomerulus.

Relaxin-induced changes in renal sodium excretion in the anesthetized male rat

Pregnancy is associated with profound changes in renal hemodynamics and electrolyte handling. Relaxin, a hormone secreted by the corpus luteum, has been shown to induce pregnancy-like increases in renal blood flow and glomerular filtration rate (GFR) and alter osmoregulation in nonpregnant female and male rats. However, its effects on renal electrolyte handling are unknown. Accordingly, the influence of short (2 h)- and long-term (7 day) infusion of relaxin on renal function was determined in the male rat. Short term infusion of recombinant human relaxin (rhRLX) at 4 μg·h−1·100 g body wt−1 induced a significant increase in effective renal blood flow (ERBF) within 45 min, which peaked at 2 h of infusion (vehicle, n = 6, 2.1 ± 0.4 vs. rhRLX, n = 7, 8.1 ± 1.1 ml·min−1·100 g body wt−1, P < 0.01). GFR and urinary excretion of electrolytes were unaffected. After a 7-day infusion of rhRLX at 4 μg/h, ERBF (1.4 ± 0.2 vs. 2.5 ± 0.4 ml·min−1·100 g body wt−1, P < 0.05), urine flow rate (3.1 ± 0.3 vs. 4.3 ± 0.4 μl·min−1·100 g body wt−1, P < 0.05) and urinary sodium excretion (0.8 ± 0.1 vs. 1.2 ± 0.1 μmol·min−1·100 g body wt−1, P < 0.05) were significantly higher; plasma osmolality and sodium concentrations were lower in rhRLX-treated rats. These data show that long-term relaxin infusion induces a natriuresis and diuresis in the male rat. The mechanisms involved are unclear, but they do not involve changes in plasma aldosterone or atrial natriuretic peptide concentrations.

Animal models of preeclampsia

There have been many attempts to produce animal models that mimic the hypertensive disorders of pregnancy, especially preeclampsia, but most are incomplete when compared to the full spectrum of the human disease. This review assesses a number of these models, organized according to the investigators attempt to focus on a specific pathogenic mechanism believed to play a role in the human disease. These mechanisms include uterine ischemia, impairments in the nitric oxide system, insulin resistance, overactivity of the autonomic nervous and/or renin-angiotensin systems, activation of a systemic inflammatory response, and most recently, activation of circulating proteins that interfere with angiogenesis. In addition a model of renal disease that mimics superimposed preeclampsia is discussed. Defining these animal models should help in our quest to understand the cause, as well as to test preventative and therapeutic strategies in the management of these hypertensive disorders of pregnancy.

Pathophysiology of pre-eclampsia: update on the role of nitric oxide

Women with chronic hypertension and pregnancy-induced hypertension are at substantial risk for developing pre-eclampsia/eclampsia, a disease with high fetomaternal morbidity and mortality. However, the etiology of this disease is still unknown. In this article, recent concepts on the pathophysiology of pre-eclampsia, with special attention to the role of nitric oxide, are reviewed.

Increased activity of cGMP-specific phosphodiesterase (PDE5) contributes to resistance to atrial natriuretic peptide natriuresis in the pregnant rat

Increased cGMP-specific phosphodiesterase (PDE5) activity in renal inner medullary collecting duct (IMCD) cells contributes to resistance to atrial natriuretic peptide (ANP) and the excessive sodium retention seen in experimental nephrotic syndrome and liver cirrhosis. Normal pregnancy is also accompanied by sodium retention and plasma volume expansion, and pregnant rats are resistant to the natriuretic action of ANP. The authors investigated a possible role of increased renal PDE5 activity in the physiologic sodium retention of normal rat pregnancy. The natriuresis and increased urinary cGMP excretion (U(cGMP)V) evoked by acute volume expansion (a measure of renal responsiveness to endogeneous ANP) was blunted in 16-d pregnant versus virgin rats, despite equivalent increases in circulating ANP in pregnants and virgins. The ANP-dependent cGMP accumulation in isolated IMCD cells from pregnants was blunted versus virgins and restored by the PDE5-selective antagonist DMPPO (10(-7) mol/L). PDE5 activity in vitro and PDE5 protein abundance in IMCD were greater in pregnants. Four days postpartum, volume expansion natriuresis, U(cGMP)V, and PDE5 protein levels in IMCD cell homogenates had returned to virgin values. These results demonstrate that normal rat pregnancy leads to in vivo and in vitro renal resistance to ANP, in association with heightened activity of the cGMP-specific PDE5 in IMCD. This may contribute to the physiologic sodium retention of normal pregnancy.

Plasma volume and blood pressure regulation in hypertensive pregnancy

BACKGROUND

Pre-eclampsia is a multisystem disorder, peculiar to and frequent in human pregnancy. It remains a leading cause of maternal and neonatal morbidity and mortality. Hemodynamic disturbances are the most prominent features of the syndrome.

PURPOSE

To provide an overview of plasma volume regulation and blood pressure control mechanisms outside pregnancy, and of the changes in normal pregnancies and in pregnancies complicated by hypertensive disorders. Furthermore, to discuss the rationale of several hemodynamic interventions.

RESULTS

In normal pregnancy, large cardiovascular changes take place. A generalized fall in vascular tone by systemic vasorelaxation causes increased blood volume, heart rate and cardiac output. In the preclinical phase, differences have been observed between normal and hypertensive pregnancies in the function of the autonomic nervous system, cardiac output and plasma volume, the volume remaining at the non-pregnant level. In the clinical phase of pre-eclampsia the typical case picture is one of a vasoconstrictive state with low plasma volume and cardiac output, high blood pressure and systemic vascular resistance in combination with signs of organ damage [proteinuria, hemolysis elevated liver enzymes low platelets (HELLP) syndrome]. Hemodynamic management is necessary in severe disease to prevent maternal complications. Management primarily focuses on pharmacological treatment of blood pressure. Clinicians make educated choices from a limited array of available drugs: beta-receptor antagonists, nifedipine, dihydralazine, methyldopa or ketanserine. Other drugs have restricted use in pregnancy. Management of low circulating volume with plasma expanders remains a subject of controversy.

Menstrual characteristics and pregnancy in women after renal transplantation

OBJECTIVES

To evaluate menstrual characteristics and pregnancy complications after renal transplantation in women of childbearing age.

METHODS

A 10-year retrospective case-control study was carried out in Esfahan Teaching Hospitals, Esfahan, Iran. The case group consisted of 50 female kidney transplant recipients of childbearing age and the control group of 100 women who were matched for age (+/-2 years) and parity with the study group. Menstrual characteristics and pregnancy data were collected by questionnaire and analyzed by chi(2) and t-tests.

RESULTS

Menstrual characteristics were improved in the 50 women who had renal transplantation, 18 of them conceived, and 20 pregnancies were evaluated. The mean interval between transplantation and pregnancy was 35.5 months and the birth weight of 44% of the newborns was less than 2500 g. Pregnancy complications included hypertension (65%), premature labor (35%) and decreased GFR (15%) during pregnancy, with a mean gestational age at delivery of 34.8 weeks. The women who conceived during the first 2 years after renal transplantation had more maternal and neonatal complications.

CONCLUSIONS

Pregnancy is possible and can be successful and safe after renal transplantation in recipients with normal kidney function. However, maternal and neonatal complications are common and occur more often in patients who conceive within 2 years of transplantation. Post-transplantation pregnancies are high risk and they should be managed in a tertiary center.

Role of nitric oxide in the natriuretic and diuretic responses in pregnant rats

Normal pregnancy is characterized by sodium conservation and increase in plasma volume, yet the natriuretic response to acute saline volume expansion (VE) is intact in pregnant rats. Nitric oxide (NO) has been suggested to play a role in renal and cardiovascular adaptations to normal pregnancy. The objective of this study was to determine the role of NO in the natriuretic and diuretic responses to VE during pregnancy. Infusion of NG-monomethyl-l-arginine (l-NMMA) was used to inhibit NO synthesis. Nine groups of Sprague-Dawley (SD) rats were studied: nonpregnant (NP-VE, n = 7), midterm pregnant (MP-VE, n = 8), and late-term pregnant (LP-VE, n = 7) SD groups that underwent VE alone after a control period; NP-l-NMMA (n = 7), MP-l-NMMA (n = 8), and LP-l-NMMA (n = 7) SD groups that were infused with l-NMMA after a control period; and another three groups of SD rats (NP-VE-l-NMMA, n = 8; MP-VE-l-NMMA, n = 7; and LP-VE-l-NMMA, n = 12) that underwent simultaneous VE and l-NMMA infusion after a control period. The change in fractional excretion of sodium was 7.22 +/- 1.03% for NPVE, 9.89 +/- 1.85% for NP-l-NMMA, and 17.66 +/- 1.85% for NP-VE-l-NMMA (P < 0.05 vs. NP-VE and NP-l-NMMA); 6.61 +/- 1.07% for MP-VE, 7.99 +/- 1.92% for MP-l-NMMA, and 10.24 +/- 1.91% for MP-VE-l-NMMA [not significant (NS) vs. MP-VE and MP-l-NMMA]; 8.20 +/- 1.92% for LP-VE, 8.09 +/- 0.70% for LP-l-NMMA, and 7.57 +/- 1.11% for LP-VE-l-NMMA (both NS vs. LP-VE and LP-l-NMMA). The increase in renal interstitial hydrostatic pressure was significantly greater in all NP compared with pregnant groups with similar experimental intervention (i.e., VE, l-NMMA, or VE-l-NMMA). In conclusion, the natriuretic and diuretic responses to VE and l-NMMA infusion were additive in NP but not in pregnant rats, indicating a possible lower ability of pregnant rats to respond to combined significant natriuretic and diuretic stimuli.

NOS inhibition restores renal responses to atrial distension during pregnancy

Nitric oxide (NO) biosynthesis increases during pregnancy and has been shown to suppress baroreceptor activity. The renal response to a simulated increase in circulating blood volume (atrial distension) is also attenuated at this time. We hypothesized that blocking NO biosynthesis during pregnancy would restore the renal response. Female rats were implanted with indwelling intracardiac balloons and central venous cannulas. After recovery, they were mated, and on day 14 of pregnancy, osmotic minipumps containing the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) or its inactive enantiomer N(G)-nitro-D-arginine methyl ester (D-NAME) (120 mg/2 ml at 10 microg/min) were implanted. In response to atrial distension (1 h), urine output increased in the D- and L-NAME-treated virgin rats. During pregnancy (day 20), this response was attenuated in the D-NAME-treated, but not the L-NAME-treated, animals, i.e., after a simulated increase in circulating blood volume, inhibition of NO biosynthesis restored the renal response of pregnant rats to that seen in virgin animals. We conclude that, during normal pregnancy, increased NO biosynthesis blunts the reflex renal response to atrial distension.

Discovery of a spontaneous genetic mouse model of preeclampsia

Preeclampsia remains a leading cause of maternal and fetal morbidity and mortality but has an unknown etiology. Women with elevated baseline blood pressure have an increased risk of this disorder. We hypothesized that BPH/5 mice, an inbred mouse strain with mildly elevated blood pressure, would develop a pregnancy-induced hypertensive syndrome. Nonpregnant female BPH/5 and C57BL/6 mice underwent thoracic aortic implantation of telemeters. After 7 days of recovery and 5 days of baseline mean arterial blood pressure (MAP) recording, strain-matched timed matings were carried out. MAP was recorded continuously during pregnancy and for 1 week after birth. In separate mice in metabolic cages, urinary protein was tracked, followed by renal histological analysis. Before pregnancy, the BPH/5 strain had elevated baseline MAP compared with the C57BL/6 strain, but both strains had similar total urinary protein levels and renal histology. MAP remained stable in both groups during the first 2 weeks of pregnancy. However, at the start of the last trimester, MAP began to rise further in the BPH/5 mice; it rose to peak levels just before delivery and returned to prepregnancy levels by 2 days after delivery. This was accompanied by late-gestational proteinuria and progressive glomerulosclerosis. No changes were observed in the C57BL/6 group except for a small decrease in MAP at mid gestation. The BPH/5 group delivered significantly smaller litters despite normal numbers of fetuses early in gestation, and longitudinal ultrasound studies documented fetal demise before the onset of hypertension and renal disease. This is the first report of an animal model that spontaneously develops a syndrome that bears close resemblance to preeclampsia, and it should have an impact on our understanding of the pathophysiology of this disorder.

Effect of 5α-pregnan-3α-ol-20-one on nitric oxide biosynthesis and plasma volume in rats

Plasma 5α-pregnan-3α-ol-20-one (pregnan) levels and nitric oxide (NO) biosynthesis increase during pregnancy. These factors have independently been implicated in the control of blood pressure and volume. We wished to determine whether pregnan might be responsible both for the increase in NO biosynthesis and for the increase in plasma volume observed during pregnancy. Virgin female Long-Evans rats were implanted with indwelling cannulas and maintained on a low nitrate/nitrite diet. After the rats recovered from surgery, 500 μg of pregnan or vehicle were given daily for 2 days. NO biosynthesis and plasma volume were measured in conscious animals before and after treatment. Pregnan caused a significant increase in NO biosynthesis (1.9 ± 0.8 μmol/24 h, n = 10) compared with the vehicle-treated control group (0.3 ± 0.4 μmol/24 h, n = 10, P < 0.05). Similarly, there was a significant increase in plasma volume in the pregnan-treated group (0.7 ± 0.2 ml/100 g, n = 11) compared with the vehicle-treated control group (0.2 ± 0.1 ml/100 g, n = 11, P < 0.05). These results confirm that pregnan can mimic pregnancy by its ability to increase both NO biosynthesis and plasma volume.

Renal interstitial hydrostatic pressure and pressure natriuresis in pregnant rats

The objective of this study was to test the hypothesis that a decrease in renal interstitial hydrostatic pressure (RIHP) accounts for the blunted pressure natriuresis during pregnancy. RIHP was measured in nonpregnant (NP; n = 9), midterm pregnant (MP; 12-14 days after conception; n = 10), and late-term pregnant (LP; 18-21 days after conception; n = 12) female Sprague-Dawley rats at two renal perfusion pressure (RPP) levels (99 and 120 mmHg). At the lower RPP level, RIHP was 5.9 +/- 0.3 mmHg for NP, 3.4 +/- 0.4 mmHg for MP (P < 0.05 vs. NP), and 2.9 +/- 0.1 mmHg for LP (P < 0.05 vs. NP) rats. The increase in RPP from 99 to 120 mmHg resulted in pressure natriuretic and diuretic responses in all groups; however, the increases in fractional excretion of sodium (DeltaFE(Na)), urine flow rate (DeltaV), and DeltaRIHP were significantly greater (P < 0. 05) in NP compared with both MP and LP rats. DeltaFE(Na), DeltaV, and DeltaRIHP were 2.06 +/- 0.28%, 81.44 +/- 14.10 microl/min, and 3. 0 +/- 0.5 mmHg for NP; 0.67 +/- 0.13%, 28.03 +/- 5.28 microl/min, and 0.5 +/- 0.2 mmHg for MP; and 0.48 +/- 0.12%, 18.14 +/- 4.70 microl/min, and 0.4 +/- 0.1 mmHg for LP rats. In conclusion, RIHP is significantly lower in pregnant compared with nonpregnant rats at similar RPP levels. Also, the ability of pregnant rats to increase RIHP in response to an increase in RPP is blunted. These changes in RIHP may play an important role in the blunted pressure natriuresis and contribute to the conservation of sodium and water that is critical for fetal growth and development during normal pregnancy.

The relation between tissue kallikrein excretion rate, aldosterone and glomerular filtration rate in human pregnancy

The changes in renal kallikrein synthesis through normal pregnancy and its relation to aldosterone excretion and the glomerular filtration rate was investigated. Overnight urinary kallikrein and aldosterone excretion rates and glomerular filtration rate were measured at 18 weeks, 34 weeks, term and postpartum in normal human pregnancy. Kallikrein excretion was raised at 18 weeks compared with the nonpregnant state (P < 0 x 001) but was significantly reduced at term. The reduction in renal kallikrein was not due to falling aldosterone concentration, which increased in the third trimester, compared with 18 weeks (P = 0 x 002) and remained elevated at term compared with the nonpregnant state (P < 0 x 001). Glomerular filtration rate remained elevated at term despite the reduced kallikrein excretion rate. These data are consistent with the hypothesis that increased aldosterone production is one factor responsible for increased kallikrein synthesis which contributes to elevated glomerular filtration rate in early pregnancy. Other factors clearly inhibit renal kallikrein production at term. In the face of plasma volume expansion associated with increased mineralo-corticoid production, the effects of reduced kallikrein synthesis at term on glomerular perfusion and reabsorption of sodium by the distal tubule may predispose to blood pressure elevation in late pregnancy.

Pregnancy in chronic renal insufficiency and end-stage renal disease

Childbearing is important to women with renal disease, but pregnancy has generally been regarded as very high risk in these women. In this review, an attempt is made to clarify the nature and severity of those risks in the settings of chronic renal insufficiency and end-stage renal disease, including dialysis patients and transplant recipients. Hypertension is the most common life-threatening problem in all three groups. A wide range of antihypertensive medications have been used, with angiotensin-converting enzyme inhibitors the only drugs absolutely contraindicated because of their association with neonatal anuria, pulmonary hypoplasia, and neonatal death. Women with serum creatinine levels of 1.4 mg/dL or greater are at risk for accelerated loss of renal function compared with women who don't become pregnant. Transplant recipients have a risk for loss of renal function similar to controls as long as renal function is well preserved. The frequency of conception is decreased in women with renal insufficiency and markedly decreased in dialysis patients (0.5% per year). Return of fertility is the rule in transplant recipients. Exposure to immunosuppressive drugs, including prednisone, azathioprine, cyclosporine, and tacrolimus, has not been associated with an increase in congenital anomalies. These drugs, particularly cyclosporine, have been associated with small-for-gestational-age babies. Transplant recipients are at risk for infections that have implications for the fetus, including cytomegalovirus, herpes simplex, and toxoplasmosis. All groups have an increased risk for prematurity and intrauterine growth restriction. The percentage of pregnancies resulting in surviving infants in women with renal insufficiency and transplant recipients ranges from 70% to 100%. For women who conceive after starting dialysis, the likelihood of a surviving infant is approximately 50%.

Temporal relationships between hormonal and hemodynamic changes in early human pregnancy

BACKGROUND

The systemic hemodynamic profile of human pregnancy is characterized by a decrease in mean arterial pressure, a rise in cardiac output and plasma volume in association with an increase in renal plasma flow and glomerular filtration rate. The factors and the time course responsible for the initial hemodynamic changes seen in human pregnancy have not been completely documented. We hypothesize that systemic and renal hemodynamic changes occur early, prior to the presence of the fetal-placental unit.

METHODS

Thirteen women were studied prior to and immediately following conception in identical fashion at gestational weeks 6, 8, 10, 12, 24 and 36. Individuals underwent mean arterial pressure, cardiac output, inulin and PAH clearance determinations.

RESULTS

Mean arterial pressure decreased by six weeks gestation (mid follicular 81.5 +/- 2.6 vs. six weeks 68.7 +/- 2.0 mm tig, P < 0.001) in association with a significant increase in cardiac output, a decrease in systemic vascular resistance and an increase in plasma volume. Renal plasma flow and glomerular filtration rate increased by six weeks gestation. Plasma renin activity and aldosterone concentration increased significantly by six weeks, whereas norepinephrine levels did not change throughout pregnancy. Atrial natriuretic peptide levels increased later, at 12 weeks gestation. Plasma cGMP levels decreased and cGMP clearance increased by six and eight weeks, respectively.

CONCLUSIONS

Peripheral vasodilation occurs early in pregnancy prior to full placentation in association with renal vasodilation and activation of the renin-angiotensin-aldosterone system. Plasma volume expansion occurs early, followed later by increases in ANP concentration, suggesting that ANP increases in response to changes in intravasular volume.

Pregnancy-induced hypertension in rats with adriamycin nephropathy is associated with an inadequate production of nitric oxide

Hypertensive complications are relatively common in pregnancy, particularly in the presence of preexisting renal disease. Although the pathogenesis of such complications is still unknown, recent animal studies have suggested that it may be related to impaired synthesis of nitric oxide (NO). Rats with adriamycin nephropathy develop a "preeclamptic-type" pregnant state characterized by elevated blood pressure, lack of hyperfiltration, and enhanced proteinuria. Preliminary studies with this model have implicated inadequate NO synthesis in the development of preeclamptic-like pregnancy. The aim of the present study was to confirm this hypothesis. Pregnant rats, both normal (PREG) and those with adriamycin nephropathy (AN-PREG), received 100 mg/L N omega-nitro-L-arginine methyl ester PO from the middle of gestation to term (day 11, term approximately 22 days). One group of AN-PREG rats received either L-arginine or D-arginine (2 g/L) from midpregnancy. At term, systolic pressure, mean arterial pressure, urinary metabolites of NO, creatinine clearance, and urinary protein were assessed. At term, compared with virgin rats with adriamycin nephropathy, untreated AN-PREG rats had increased systolic pressure, mean arterial pressure, and proteinuria (mean arterial pressure, 124 +/- 2.5 versus 99.7 +/- 1.6 mm Hg [P < .05]; proteinuria, 434 +/- 58 versus 216 +/- 63 mg/d [P < .05]). Creatinine clearance did not change (1.68 +/- 0.23 versus 1.35 +/- 0.09 mL/min, P = NS). In PREG rats, urinary metabolites of NO increased approximately threefold at term pregnancy compared with control. By contrast, in AN-PREG rats, excretion of urinary metabolites of NO increased only by approximately 1.7-fold (P < .01) versus PREG rats. With the exception of AN-PREG rats, inhibition of NO synthesis with N omega-nitro-L-arginine methyl ester enhanced blood pressure and decreased creatinine clearance but did not influence proteinuria. Excretion of urinary metabolites of NO was similarly inhibited in all rats. In AN-PREG rats, L-arginine normalized blood pressure (91 +/- 2.15 mm Hg) and lowered proteinuria partially but significantly. D-Arginine had no effect. In summary, AN-PREG rats are unable to adequately increase NO synthesis when physiologically required. Correction of this deficit by L-arginine treatment induced a significant clinical improvement.

Glomerular actions of nitric oxide

NO, a simple molecule synthesized from L-arginine by NO synthases, has been identified to play an important role in cell communication, cell defense and cell injury. The half life of NO is very short because NO either reacts with superoxide anion (O2-), and/or binds to heme molecules or Fe-S groups present in proteins. The biological effects of NO depend on both the concentration of NO at the site of action as well as upon the specific location where NO is generated. Small quantities of NO are generated by cNOS such as that present in the vascular endothelium, while large quantities of nitric oxide are synthesized by iNOS in response to cytokines or bacterial products. Within the kidney NO generated by endothelial cNOS participates in the regulation of the glomerular microcirculation by modifying the tone of the afferent arteriole and mesangial cells (Fig. 4). In addition, NO generated by macula densa and the afferent arteriole control glomerular hemodynamics via TGF and by modulating renin release. Therefore NO is important in the physiologic regulation of glomerular capillary blood pressure, glomerular plasma flow and the glomerular ultrafiltration coefficient. Through its actions on glomerular pressures and flows, NO may also regulate the macro- and micromolecular traffic through the mesangium. Chronic NO insufficiency causes hypertension and glomerular damage and may be causally involved in the genesis of salt dependent hypertension. Increased NO production may be involved in the early pathogenic hemodynamic changes in diabetes and in the physiologic hemodynamic responses to normal pregnancy. Maintenance of the antithrombogenic properties of the endothelium is another important action of NO which inhibits platelet aggregation and adhesion. Large quantities of NO such as that synthesized by either glomerular cells or macrophages during glomerular inflammation may lead to glomerular injury. A better understanding of the physiology and pathophysiology of NO in the kidney will lead to the development of new therapeutic avenues.

Effect of pregnancy on the long-term function of renal allografts: an update

In 1992 we published a case-controlled study of posttransplant follow-up in 36 renal allograft recipients (Am J Kidney Dis 19:167-172, 1992). Eighteen of these patients became pregnant and comprise the index group; the 18 patients who did not become pregnant were considered controls. By the end of the follow-up period, plasma creatinine in the index group and controls had increased by 19% and 8%, respectively. Graft loss or chronic rejection occurred in one patient in the index group and in two in the control group. As there were no significant differences between the two groups, we concluded that pregnancy was unlikely to have a major effect on long-term graft function and/or survival. Subsequently, a case control study of Finnish women demonstrated graft survival favoring women who never conceived versus those who did (69% v 100%, respectively; P < 0.005) and thus prompted us to extend our posttransplant follow-up by a further 3 years. Data are currently available for 17 index subjects and 17 controls and during the entire follow-up period, graft losses have occurred in one index subject and in four controls. Plasma creatinine at the end of the follow-up period (1.40 +/- 0.52 mg/dL and 1.54 +/- 0.95 mg/dL, respectively) had increased from 3 years earlier by 11% and 7%, respectively, increments across time that were not significant. Although the increase in plasma creatinine was greater in the index subjects compared with the controls, there were no significant differences between the two groups. While our data do not exclude a minor deleterious effect of pregnancy on long-term graft function, we believe that female allograft recipients can be reassured that pregnancy is unlikely to substantially alter long-term graft function.